An Agitator is a machine used in a tank for mixing various process media’s together, this includes water, solvents, dissolvable solids or non-dissolvable solids, gas or heat transfer. Many process operations involve fluid mixing such as; liquid-solid mixing, gas-liquid mixing, liquid-liquid mixing, blending of mixable liquids, and also fluid motion.
What is the purpose of an agitator?
An Agitator is used for mixing different process media – Chemical Addition or Pharmaceutical Ingredients. An agitator is also used in the Water Industry for adding various chemicals to bring the source water up to drinking water standards, i.e., Lime, Acids, Coagulants, Flocculants, Powder Activated Carbon, Soda Ash, Aluminium Sulphate, Lime reduces the Acidity of the Water, Sulphuric Acid is used bring down the Alkalinity, Coagulants and Flocculants are used to draw any solids present in the water into clumps that will float on the surface and can then be removed.
What are the various parts or components of an agitator?
An Agitator is made up of a shaft with impellers, mechanical seal (single dry running seal, double seal either wet (liquid lubricated) or dry (gas lubricated) or a lip seal or stuffing box, both of these are only suitable for Atmospheric Vessel (no pressure), motor and gearbox.
An agitator shaft is the connection to the drive unit (motor & gearbox) and where the impellers used for the mixing are welded or bolted onto.
What are the different types of agitators and their selection criteria?
90% of Agitators are a Top Entry Agitator , the remaining 10% include other options such as; Bottom Entry Agitator, Side Entry Agitator and Bottom Entry Mag Drive Agitator.
The main advantages of a Top Entry Agitator is that it can handle a larger variance in viscosities and specific gravities and also the fact that the mechanical seal is not in the liquid.
Bottom Entry Agitators have the mechanical seal in the process liquid and you can get leakage of the process media if the mechanical seal fails.
Side Entry Agitator also have the mechanical seal in the process liquid and if the mechanical seal fail, the process media will leak out through the seal.
Side Entry Agitators really don’t carry out any mixing, they are more commonly used in Large Storage Tanks to keep the process media moving, examples are Milk Storage Tanks to keep the milk cool.
They are also used in large Beverage Tanks to keep the product moving, examples are Orange Silos & Cider Tanks etc Pharma companies also use them in their Water Treatment Plants.
Regarding the selection criteria, it is the customer who decides which type of Agitator or Tank Mixer is required for their process.
The applications generally fall under the following main headers (but is not limited to):
- Heat transfer
- Continuous reaction
Depending on the industrial sector the customer is in, the mechanical & material suitability for each application can differ greatly. Each of the applications have a typical impeller type that is suited to deliver the turbulence necessary to mix the ingredients.
What are tank mixers? How do you size a tank mixer?
Tank mixers are the same as tank agitators which is an agitator mounted on a tank to aid process operations with fluid mixing.
Tank mixers are sized when the customer fills out a data sheet for the specific Tank and Agitator which states the Tank Dimensions & Duty Requirement, Design & Operation Temperatures & Pressures, whether it is a Safe Area Operation or if Atex is Applicable and Duty requirement, Duties, Liquid-Liquid Mixing, Liquid-Solid Mixing, Dissolution of Soluble Solids, Solids Suspension, Powder Addition, Heat Transfer and Gas Induction.
What is a slurry agitator?
A slurry is any liquid with some solids contained in the solution. A slurry agitator can handle such liquids,
In the Pharma sector, the solids would be the product / active ingredient which is then further processed via a filter dryer to leave the powder. In the waste-water treatment sector, a slurry will have higher solids content that is transferred for de-watering. A slurry agitator is often used to keep the solids in suspension to prevent settling out and forming on the base of the vessel or bulk tank before being transferred to the next stage of processing.
What are the various agitator impeller types?
Standard Hydrofoils: these impellers are axial flow high efficiency general purpose – they are designed to offer mixing with low Power requirements. They are also low shear and will not damage sensitive process media.
Wide Blade Hydrofoils: these impellers are axial flow high efficiency – general purpose – they are designed with higher pumping in mind in comparison to the Standard Hydrofoils impellers. They are low shear and they use more power however they would still use less power in comparison to the Pitched or Straight Blade Turbines.
Pitched Blade Turbines: are high pumping axial flow impellers, they are high shear so that could damage sensitive Process Media.
Straight Blade Turbines: are radial flow impellers, they are also high shear and are used for suspending solids where uniform suspension is required or for moving heavy liquids off the bottom of Tanks.
RCI (Retreat Curve Impellers): can be used on Glass Lined Tank/Agitators, they offer lower shear than the Straight Blade Turbines with lower power requirements. They are usually used as a Bottom Impeller because they can be positioned very close to the curve of the bottom dish of the Tank, the blades curve upwards and they are also curved towards the end of the blades.
Gas Dispersion Impellers: are used for Mixing Gas into Liquids.
Rushton Turbine: is a gas dispersion impeller for mixing Gas into Liquids, it is an older design, not as efficient as more modern designs such as the Chemineer BT-6 and CD-6.
Saw Tooth Disk or Dispersion Blade Impeller: is used for High Shear applications as they create lots of turbulence for breaking down solids.
Agitator sizing – how do you correctly size an agitator?
To size an agitator, you first need to know what are the tank dimensions and duty Requirements.
Usually the customer knows their Process and will request the type of Agitator and impeller types, they will also specify the Duty, Liquid, Liquid Mixing, Suspend Solids, Dissolve Solids, Heat Transfer, Gas Dispersion also the type of Mixing required, Gentle, Medium or Vigorous.
Gearbox selection for an agitator – again, its down to the Duty requirement and Tank Size.
What is the difference between an agitator and a mixer?
There is no difference really, some people classify Agitators as mechanically driven Mixers, and some people classify Mixers as Non Mechanical Driven Agitators, i.e. Static Mixers, which have no moving parts but will also mix liquids.
What is the difference between an agitator and a reactor?
The Agitator is for Mixing the Contents of Reactor Vessels.
Which type of agitator is used for viscous liquids?
The customer will advise which agitator they require, it could be an Anchor Type Impeller or a Helix or Speciality Impellers like the Chemineer JT-2.
Batch mixing versus Continuous mixing?
- Batch mixing – if you need residence time for reaction, crystallisation, or storage capacity for downstream processing.
- Continuous mixing – if you have fast reactions or a fully continuous manufacturing process.
- Semi batch – using batch stirred tank vessels in combination with recirculation loops with static mixers or rotor stator mixers.
Which type of Mixing Technology does Flexachem provide?
Flexachem has over 30 years of expertise in fluid mixing knowledge supported by application software and proprietary mixer designs.
- Batch mixing – top, side, bottom entry or magnetic drive agitators.
- Batch/continuous mixing – high shear rotor stator mixers.
- Continuous mixing – low or high shear static mixers
All the above arrangements come with a wide array of impeller technologies to suit your needs. These technologies handle all fluids from low to high viscosity, low to high sheer sensitivity and a full array of pH conditions. (Safe area/ ATEX).
Chemineer and Inoxpa are manufacturers of Agitators and Mixing Products for customers worldwide in the chemical, pharmaceutical, biotechnology and food & beverage processing industries and water & waste water treatment plants.
PRG specialise in Magnetic Drive Agitators and have highly experienced engineering specialists who can create bespoke solutions for any application. Their design not only offers an excellent clean-ability and surface quality but also a long natural life of the equipment components and a minimum of maintenance.
For simple applications, we use Prodomix mainly in the Water Industry e.g simple mixing for water like process media and in the Food & Paint Industries – it is always open tank applications without a Mechanical Seal.
How Chemineer’s CFD Modelling software helps?
- Models power draw and pumping capacity for multiple impeller types and sizes
- Analyses gas dispersion, ability to suspend solids, blend times.
- Does parallel mechanical design checks on shaft stresses, gearbox bearings and gear life
- Checks shaft critical speeds (harmonic frequencies)
- Integrated 2D CFD modelling
- Flexachem Mixing Specialist is fully trained in using the software.
We strive to ensure our clients are offered the latest technology to improve the performance of agitation and mixing systems in their processes.
If you have a particular application for an agitator / tank mixers and would like assistance in the sizing of the equipment, please complete these forms and submit them to our product specialists as a preliminary basis to aid your discussion:
Michael Bradley (External)
Ken Killoughy (Internal)
Ross O’Donovan (Internal)
Tel: 021 4617260
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